1. Field of the Invention:
This invention relates in general to tension leg platforms for offshore drilling, and in particular to a top connector for connecting the upper end of a tendon to the platform.
2. Description of the Prior Art:
A tension leg platform is a type of offshore drilling and production structure. The platform floats and is secured to the sea floor by tendons. The tendons are large pipes, about 20 inches in diameter. After securing the tendon to the platform and to the sea floor, ballast water is pumped out to cause the platform to rise. This is resisted by the tendons, placing the tendons under high tension load. The tendons under tension provide a stable platform for drilling and oil production.
In U.S. Pat. No. 4,871,282, Charles E. Jennings, Oct. 3, 1989, a connecting device is shown that will connect the top of the tendon to the platform. In that device, the upper end or terminal segment of the tendon has helical threads. The threaded section extends through a housing which has a conical bore. Segments, or dogs, will slide down the conical bore from a retracted position to an engaged position. The segments have mating threads which will engage the threads on the tendon. A cam ring causes the downward movement of the segments. The cam ring also will rotate the segments once in contact with the tendon to engage the threads of the segments with the threads of the tendon.
While the design shown in U.S. Pat. No. 4,871,282 is workable, it is important that the position of the thread helixes of the segments match each other in order for the segments to radially engage the threads of the tendon. If the threads do not match those of the other segments, either the relative axial location or circumferential positioning between the segments must be adjusted. Axial adjustment of the tendon relative to the housing is often impractical and difficult. Aligning the particular segments circumferentially can be time consuming in order to match the helical threads of the segments.